Structure of Q.931 message (Release)
Message type: RELEASE
Significance: Local
Direction: Both
Info Element Direction Type Length
Protocol   Both   M   1
      discriminator
Call reference   Both   M   2-
Message type   Both   M   1
Cause   Both   O   2-32
Display   n ® u   O
Signal   n ® u   O   2-3
Cause description may require many bytes